Discoveries

May 03, 2023

The Sleep of Seals

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Elephant seals have some strange sleeping patterns, Cosmos Magazine reported.

The marine mammals can sleep more than 10 hours per day when they’re on land during breeding season. But scientists have wondered if the seals get any shut-eye during months-long foraging trips in the Pacific Ocean.

It turns out that they do, but not a lot, a new study found.

A research team figured that out after recently scanning the brains of 13 elephant seals using an electroencephalograph (EEG) system that could track the seals’ brainwaves while they were at sea. They also equipped the seals with some depth recorders and accelerometers to track their movements.

The researchers discovered that the animals can function on just two hours of sleep per day out at sea. They achieve this by taking 10-minute naps during their deep dives, spiraling gently toward the sea floor.

Data from 104 sleep dives showed that the seals went into “slow-wave sleep” – a deep sleep stage – while gliding downward, then changed to rapid-eye-movement (REM) sleep.

“It doesn’t seem possible that they would truly go into paralytic REM sleep during a dive but it tells us something about the decision-making processes of these seals to see where in the water column they feel safe enough to go to sleep,” said co-author Terrie Williams.

Williams and her colleagues noted that the finding makes the creatures one of the least sleepy mammals in the world.

Meanwhile, they added that the EEG device could also aid in conservation efforts by helping scientists learn more about the places where endangered animals sleep.

This story originally appeared in the May 03, 2023 newsletter, Demography and Destiny.